Title: Estimates of nitrous oxide emissions from motor vehicles and the effects of catalyst composition and aging.

Principal Investigator / Author(s): Winer, Arthur M.

Contractor: UC Los Angeles

Contract Number: 02-313

FTIR spectroscopy was used to determine nitrous oxide concentrations in dilute exhaust samples collected from vehicles tested as part of the last two California vehicle surveillance programs. We conducted more than 400 dynamometer experiments for 134 light-duty vehicles, including passenger cars and light-duty trucks. In addition to exhaust species concentrations, we collected exhaust and catalyst temperature data, fuel sulfur content, and air-to-fuel ratio data. Type of vehicle, driving cycle, applicable emissions standard, and especially catalyst temperature were found to be the most important factors determining N2O emissions from gasoline powered light-duty vehicles. In all cases, the highest catalyst temperature range ( > 650 °C) was associated with lower nitrous oxide emission factors whereas intermediate catalyst temperatures (120 °C to 550 °C) were associated with elevated N2O emissions, and little or no emissions were observed below 120 °C. The mean nitrous oxide emissions factor from all vehicles tested was 20 mg km -1 (N = 264; ó = 22), lower than reported in previous research. The current trend of decreasing N2O emissions from light-duty vehicles is expected to continue as the result of increasingly stringent emission standards for NOx. Long lifetime catalysts and reduced traffic congestion will also result in decreased N2O emissions.